title: Ultrafast refractive index control of a terahertz graphene metamaterial.
abstract: Modulation of the refractive index of materials is elementary, yet it is crucial for the manipulation of electromagnetic waves. Relying on the inherent properties of natural materials, it has been a long-standing challenge in device engineering to increase the index-modulation contrast. Here, we demonstrate a significant amount of ultrafast index modulation by optically exciting non-equilibrium Dirac fermions in the graphene layer integrated onto a high-index metamaterial. Furthermore, an extremely-large electrical modulation of refractive index up to Δn ~ -3.4 (at 0.69 THz) is achieved by electrical tuning of the density of the equilibrium Dirac fermion in the graphene metamaterial. This manifestation, otherwise remaining elusive in conventional semiconductor devices, fully exploits the characteristic ultrafast charge relaxation in graphene as well as the strong capacitive response of the metamaterial, both of which enable us to drastically increase the light-matter interaction of graphene and the corresponding index contrast in the graphene metamaterials.
authors.affiliation: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-751, Republic of Korea.
authors.forename: Seung Hoon
authors.initials: SH
authors.lastname: Lee
authors.forename: Jeongmook
authors.initials: J
authors.lastname: Choi
authors.forename: Hyeon-Don
authors.initials: HD
authors.lastname: Kim
authors.forename: Hyunyong
authors.initials: H
authors.lastname: Choi
authors.forename: Bumki
authors.initials: B
authors.lastname: Min